Simplify creation of issues over email

Problem to solve

Make using gitlab via email more convenient.

Intended users

Developers.

Further details

Implementing this feature improves integration of gitlab with email-based and offline workflows.

Proposal

Currently, it is possible to create issue via email by sending message to special email address. Unfortunately, the only way to know that email address is to web interface.

What is more, this email is unique to every repository, so if I want to work over email, I have to fetch one email for every repository I plan to contribute ever. I see two solutions to described problem:

(preferred) Make it single address, and dispatch based on email header, like following:

To: user-secret-address@gitlab.com
Subject: [gitlab-org/gitlab-c] Title of new issue

Body of new issue.

(less preferred) Leave multiple addresses as is, but make it possible to retreive them via API.

Permissions and Security

No security implications, as far as I know.